Everyday, manufacturers, machinists, welders, and mechanics may use torque wrenches which allow them to measure and apply torque to a fastener so that the fastener may meet proper tension and loading requirements. A more sophisticated method of presetting torque may include a calibrated torque indication mechanism. The most common form may use an over-center or “click” mechanism which may allow the wrench handle to rotate a few degrees in relation to the head of the tool, with a tactile and audible click when the desired torque is attained.
These torque wrenches may be typically affected by hand-hold position errors. These inaccuracies may be caused by application of force on the handle at locations other than at its centerline, which may affect the bending moment in the handle differently than the torque applied to the fastener. These, inaccuracies may increase in severity when the applied force approaches the wrench click pivot, or as the click pivot is moved farther away from the fastener axis. This design issue may particularly affect tubing torque wrenches where the click or breakaway axis may be significantly offset from the fastener due to physical constraints. The magnitude of these inaccuracies may be as high as 300% based on tool configurations currently in use in industry.
Current click-type torque wrenches may come in two primary configurations: A square drive or ratchet end, and a configuration allowing for the attachment of interchangeable wrench heads. The square drive configuration may be used most commonly with drive sockets, adapters and/or extensions. Interchangeable wrench heads may allow straight-on access to the fastener and utilization of specialty heads for limited access applications. Both configurations may allow for rotation of the wrench handle in a plane substantially normal to the fastener axis of rotation. Correction factors may be necessary with some adapters to maintain application of the proper torque. Universals may be used in line with the drive socket for certain circumstances at up to a 15 degree angle. When it is not possible to access a fastener with a calibrated torque wrench due to the restrictions cited above, there is also a “Two Flats Method” that may be used. This method may require the mechanic to rotate a tube B-nut a prescribed angle, commonly 120 degrees, past hand tight.
The accuracy of existing solutions may depend on the mechanic to apply force at a particular point on the handle, commonly called the “load point”. The load point is the location at which the force was applied during calibration of the tool. As noted earlier, applying force at a location other than the load point may result in decreased accuracy of the applied torque. Applying force at the load point is difficult to consistently achieve in practice, due to many factors such as limited access, training, fatigue, etc. Some solutions may incorporate a torque measurement device in-line with the fastener axis. These systems do not suffer from inaccuracies noted above, but commonly may suffer from fastener access issues. These methods are not applicable to tube torque operations where the axis of the fastener is not available because the tube is in the way. Other existing solutions for lack of right angle access to the fastener such as adapters, extensions and crows feet, may be cumbersome, time consuming and prone to error.
In addition, calibrated torque tools typically cannot be hinged near the head because this often causes the indicated torque to be in error in proportion to the cosine of the angle between the wrench head and handle. This may necessitate rigid wrench designs and right angle access to the fasteners. In many areas this access may not be available, especially in tube installations where a variety of constraints affects fastener orientation. A need therefore exists to provide a wrench that overcomes the above-described limitations.